1. Field of the Invention
This invention relates to a bearing having a self-lubricating liner and, more specifically, a liner containing a resin matrix including therein a dispersion of fluorocarbon particles having a low coefficient of sliding friction and graphite fibers.
2. Description of the Prior Art
Although, traditionally, bearings have been lubricated by liquid lubricants such as oil, it has been felt that attendant problems with the use of liquid could be avoided through the use of dry lubricants in the form of a bearing liner. Some noteworthy efforts to provide a bearing have a self-lubricating liner include, for example, those disclosed in U.S. Pat. Nos. 2,988,397; 3,198,691, 3,471,207; and 3,549,049. These disclosures teach the use of a liner containing an adhesive resin matrix which includes therein a random dispersion of self-lubricating fluorocarbon particles. These particles are intended to provide the low coefficient of sliding friction essential for a bearing surface while the resin provides a means of supporting the particles and insuring their adherence to the bearing member.
Although they have the desired low coefficient of sliding friction, there are other properties of the fluorocarbon particles which limit their broader application as a bearing liner material. The self-lubricating fluorocarbon material most often used, for example, is Teflon (a trademark of the DuPont Corporation for polytetrafluoroethylene) which has demonstrated a tendency to deform or extrude when subjected to higher load conditions at temperatures around 325.degree. F. As a result, when utilized during these operating conditions, there is increased wear of the bearing liner and a corresponding decrease in its effective life. This general problem is further aggrevated by the fact that the fluorocarbon material also has a relatively low thermal conductivity which interferes with the desired dissipation of frictional heat under these more critical operating conditions. Although the resin matrix does allow some beneficial heat transfer and does make some contribution to the overall strength of the liner, it is not primarily chosen for its heat transfer or strength capabilities but rather for its ability to support the particles without disturbing the low coefficient of sliding friction provided by the particles and essential in a self-lubricating bearing.
It has generally been recognized that the use of graphite in the resin matrix might be desirable since it too is a self-lubricating material and has heat transfer characteristics and resistance to wear which are better than those of fluorocarbon. A number of attempts have heretofore been made to introduce graphite in the form of powder or flakes within the matrix to improve the wear properties of the liner. Examples include some of the above-cited patents and U.S. Pat. No. 3,238,601. However, since graphite has a higher and, therefore, less desirable coefficient of sliding friction than fluorocarbon, the amount of graphite powder utilized has been limited with respect to the amount of fluorocarbon particles utilized in an effort to optimize the desirable properties of each. The overall improvement in strength and wear resistance at normal operating temperatures and loads of a bearing liner including the graphite powder has accordingly been limited by this balance. These improvements in the liner for normal operating conditions are not as significant if the liner is operated at the same higher temperatures and under the same heavier work loads that would result in its failure, as discussed above, if no graphite were present.
As a result, although generally recognizing the strength and wear limitations of these self-lubricating liners at higher operating temperatures and load conditions, the above-cited patents do not particularly address themselves to a means of effectively improving the bearing liner for use throughout the wider range of desired operating conditions.